元类相关试题
一、在元类中控制把自定义类的数据属性都变成大写
class Mymeta(type):
def __new__(cls, name,bases,dic):
attr = {}
for k,v in dic.items():
if not k.startswith('__'):
k = k.upper()
attr[k] = v
attr[k] = v
return type.__new__(cls,name,bases,attr)
class People(metaclass=Mymeta):
school = 'oldgirl'
addr = 'shanghai'
def __init__(self,name,age):
self.name = name
self.age = age
print(People.SCHOOL)
print(People.ADDR)
二、在元类中控制自定义的类无需init方法
class Mymeta(type):
def __call__(self, *args):
obj = self.__new__(self)
obj.name = 'nick'
obj.age = 19
return obj
class People(metaclass=Mymeta):
pass
p = People()
print(p.name)
三、在元类中控制，把自定义的类的数据属性都放到attr字典中
class Mymeta(type):
def __new__(cls, name,bases,dic):
dic2 = {'attr':{}}
for k,v in dic.items():
if not k.startswith('__'):
dic2['attr'][k] = v
return type.__new__(cls,name,bases,dic2)
class People(metaclass=Mymeta):
school = 'oldgirl'
addr = 'shanghai'
def __init__(self,name,age):
self.name = name
self.age = age
print(People.attr['school'])
print(People.attr['addr'])
四、四种方式实现单例模式
## 第一种
PORT = 3306
HOST = '127.0.0.1'
class Sql:
instance = None
def __init__(self,port,host):
self.port = port
self.host = host
@classmethod
def get_sigo(cls):
if not cls.instance:
cls.cls(PORT,HOST)
return cls.instance
## 第二种
PORT = 3306
HOST = '127.0.0.1'
def get_sigo(func):
instance = None
def wrapper(*args,**kwargs):
if len(args) != 0 or len(kwargs) != 0:
#表示传了参数，生成新对象
res = func(*args,**kwargs)
return res
else:
nonlocal instance
if not instance:
instance = func(PORT,HOST)
return instance
return wrapper
@get_sigo
class Sql:
def __init__(self,port,host):
self.port = port
self.host = host
## 第三种
PORT = 3306
HOST = '127.0.0.1'
class Mymeta(type):
def __init__(self,name,bases,dic):
# 把实例化好的对象，放到类的名称空间
self.instance = self(PORT,HOST)
def __call__(self,*args,**kwargs):
if len(args) != 0 or len(kwargs) != 0:
obj = object.__new__(self)
obj.__init__(*args,**kwargs)
return obj
else:
return self.instance
class Sql(metaclass = Mymeta):
def __init__(self,port,host):
self.port=port
self.host=host
## 第四种
# sigo 文件
# ************************************
PORT = 3306
HOST = '127.0.0.1'
class Sql():
def __init__(self,port,host):
self.port=port
self.host=host
s1=Sql(PORT,HOST)
# ************************************
def test():
from sigo import s1
print(s1)
def test2():
from sigo import s1 as s2
print(s2)
